The PS-341 dose is increased in successive groups of at least 3 patients until the highest dose that can be given safely with radiation is reached. Patients who develop severe side effects from the drug temporarily stop taking it to allow the side effects to improve. If needed, the dose may be decreased. Radiation therapy may also be stopped temporarily in patients who develop severe effects on the mouth, throat or skin. Side effects may be treated with increased fluid (by mouth, stomach tube, or vein), anti-nausea or anti-diarrhea medications, pain medications and medications to boost red or white cell counts or platelets. The drug Florinef may be given to help regulate body fluids and blood pressure.